This invention relates to a method of manufacturing high strength low alloys steels with low temperature toughness, more particularly to a method capable of greatly improving the strength and toughness by an accelerated cooling treatment following hot rolling.
Various methods of improving the strength and toughness of high strength low alloy steels have been proposed. Among these methods, thermomechanical treatment of the low alloy steels is important in view of economy and characteristics of the products, and accelerated cooling subsequent to hot rolling of thick plates is also important. Furthermore, controlled rolling technique is widely used for the purpose of improving the strength and toughness of low alloy steels, and it has been known that the accelerated cooling subsequent to the controlled rolling is effective to further improve the strength without impairing toughness. According to these known methods, however, it has been difficult to simultaneously improve the strength and toughness by the accelerated cooling after hot rolling. Especially, when a great improvement in the strength is contemplated by the accelerated cooling treatment, it has been necessary to sacrifice the toughness.